Seasonal changes in quantity and composition of suspended particulate organic matter in lagoons of the Alaskan Beaufort Sea

Estuarine ecosystems in the Arctic are subject to extreme seasonal changes in the physico-chemical environment, but multi-season studies of these near-shore systems are relatively scarce. We measured bulk concentrations, fatty acids, pigments, and bulk delta C-13 and delta N-15 of suspended particulate organic matter (POM) collected from lagoons along the Alaskan Beaufort Sea coast during full-ice cover (April), ice break-up (June), and open water (August) and found that the quantity, composition and sources of suspended POM vary widely among seasons. We saw a shift across all lagoons from (1) low concentrations (80 mu g C l(-1)) and predominantly refractory material in April to (2) high concentrations (>500 mu g C l(-1)) with new inputs of organic matter from diatom production and river sources in June to (3) a consumer-, dinoflagellate- and/or green algae-influenced system in August. Relatively low delta C-13 values in all seasons (<=-25%) suggest that terrestrial material was a major component to the POM pool throughout the year. Concurrently, fatty acid and pigment profiles show varying inputs of primary producers among seasons, with higher diatom relative to dinoflagellate contributions in June and vice versa in August. Elevated 22:6 omega 3/20:5 omega 3 (docosahexaenoic acid/eicosapentaenoic acid) ratios and polyunsaturated fatty acid proportions in the lagoons during August indicate that POM from lagoons provides animals with essential nutrients. These results demonstrate that the compositions and sources of organic matter available to consumers are a product of the dynamic seasonality of these ice-dominated, yet productive Arctic estuarine ecosystems.